Inlet cone device and method

ABSTRACT

1,143,295. Pipe couplings. LUMMUS CO. 12 May, 1967 [13 May, 1966], No. 22215/67. Heading F2G. [Also in Division F4] In an installation for the production of olefins from hydrocarbons such as ethane and propane, the outlet 10 from a cracking heater is connected to a shell and tube heat exchanger 14 by a connecting duct 12 comprising a conduit 24, which has a cross-section that increases along its length and is connected around its periphery at its larger end to the heat exchanger shell, a bank of tubes 30 engaging one with each of the heat exchanger tubes 46, the ends of said tubes 30 being sealing secured within the narrower part of said conduit, and a supply pipe 36 connected to the conduit and capable of supplying steam to the region of conduit interior between the heat exchanger and the said secured ends of the tubes 30. The tubes 30 are secured in the narrow part of the conduit by a convex, concave or flat tube sheet 28. Alternatively, Fig. 2 (not shown), hexagonal tube ends are welded together to form a honeycomb structure which  is sealed in the narrow part of the conduit by shield of metal or of refractory or other suitable packing material. Insulating material 26 is provided between the conduit inlet and tube sheet. The conduit may be conical as shown, pyramidal or tetragonal.

March 26, 1968 w. TUCKER 3,374,832

INLET CONE DEVICE AND METHOD Filed May 13, 1966 INVENTOR William Tucker ATTORNEYS United States Patent Ofitice 3,374,832 Patented Mar. 26, 1968 3,374,832 INLET CONE DEVICE AND METHOD Wiiliam Tucker, Great Neck, N.Y., assignor to The Lummus Company, New York, N.Y., a corporation of Delaware Filed May 13, 1966, Ser. No. 549,852 8 Claims. (Cl. 165-134) ABSTRACT OF THE DISCLOSURE This invention relates to a novel inlet device for connecting the output of a cracking heater with the inlet of a transfer line heat exchanger, and a method of operating the same. In essence the present invention comprises the combination of a plurality of inlet cone tubes, the majority of said tubes being loosely slip-fitted into exchanger tubes, together with an inert fluid purge of the space between the exchanger tube sheet and inlet cone tube sheet, the inert fluid being supplied at a higher pressure than the heater efliuent. In an alternate embodiment, the inlet cone tube sheet is eliminated by utilizing hexagonal tubes welded to each other. The inert fluid effectively purges the cone area of any hydrocarbon which may enter, and because of the slip-fit of the inlet cone tubes within the transfer line exchanger tubes, the inlet fluid may pass around the outside of the inlet cone tubes and into the exchanger tubes.

This invention relates to a novel inlet device for connecting the output of a cracking heater with the inlet of a transfer line heat exchanger, together with a method of operating the same.

In the production of olefins from normally gaseous hydrocarbon by thermal cracking or in the steam reforming of naphtha and the like, it is necessary that the reaction products be cooled very quickly from the cracking temperature to a temperature below the point where secondary reactions can proceed. Such secondary reactions decrease yield and cause coke formations which decrease the length of time a heater can be kept in service. In conventional practice, the heater effluent is passed in a conduit to a heavily insulated inlet cone which is in direct communication with the tube side of a transfer line exchanger (also referred to as a cracked gas cooler), the cone being necessary because of the substantially larger diameter of the exchanger. The insulation, which may be internal or external, is provided in an attempt to keep the gas as hot as possible until it actually reaches the eX- changer. It is also possible to cool the efliuent directly by injection of a suitable cooling medium but while this effects the desired cooling very rapidly, it results in a significant loss of recovered high pressure steam. As a result, indirect cooling in a transfer line exchanger is V generally preferred.

Operating experience has demonstrated that for certain feedstocks, particularly ethane and propane, and for high severity naphtha cracking, the inlet cone is the most criti cal zone for coke buildup in the entire heater-transfer line system. This is apparently due to the flow characteristics of the hot gases within the cone. Coke may build up on the walls of the cone and eventually break off, causing blockage of gas flow through a portion of the exchanger. Further, it is difficult to distribute the flow to all of the exchanger tubes equally; tubes with low gas flow tend to foul quickly. Ultimately, the resulting high pressure drop requires that the whole heater-exchanger system be shut down and the cone and tubes cleaned out, even through there may be essentially no coke buildup in the heater itself.

High severity pyrolysis requires extremely rapid cool ing and very low pressure drop across the cooler. This is accomplished by providing many parallel tubes of small diameter, but such an arrangement demands that the inlet cone have a large volume. This turns the inlet cone into an adiabatic reactor, the same as a large or long transfer line. The adiabatic reaction is contrary to the principles of short residence time cracking, and reduces the temperature and causes coke formation, increasing pressure drop and shortening run length.

The area of the heater outlet tubes is typically about one-half of the area of the exchanger tubes, and with a conventional inlet cone the volume thereof may be as much as one third of the volume of the heater coil. Since discharge from the heater is at maximum temperature, the adiabatic reaction is rapid, with a significant effect on yield and coke formation.

Prior workers have addressed themselves to this problem, but a truly satisfactory solution has been elusive. It has been suggested, for example, to weld extensions onto the exchanger tubes and bring them close together near the narrow end of the cone, the object being to get the gas into the exchanger tubes without any opportunity for turbulent flow in the cone area, and to reduce adiabatic reaction by reducing cone volume. With such a design it is possible for gas to enter between the tubes and deposit coke, causing tube deformation and, ultimately, failure. A second disadvantage of this design in that it is often not desirable to weld the inlet cone tubes to the exchanger tubes, because this can impose restrictions on the free movement of the tube sheet and impose thermal stress. This is particularly true with ethane-propane feedstocks, where water-cooled fixed tube sheet exchangers are preferred, and the tube sheet must remain flexible.

It is thus a general object of the present invention to prevent coke buildup in the inlet cone between a heater and a transfer line exchanger.

Another object of the invention is to provide an improved inlet cone for connecting a heater to a transfer line exchanger.

Still another object of the invention is to provide a novel method of transferring cracked gas from a heater to a transfer line exchanger.

Yet another object of the invention is to provide means for passing cracked gas from a heater to a transfer line exchanger which effectively prevents coke buildup and which does not involve welding all of the tube extensions onto the exchanger tubes.

A still further object of the invention is to pass cracked gas from a heater to a transfer line without coke buildup, without reducing yield and without loss of heat recovery potential.

Various other objects and advantages of the invention will become clear from the following detailed description of several embodiments thereof, and the novel features will be particularly pointed out in connection with the appended claims.

In essence, the present invention is based on the combina-tion of inlet cone tubes, the bulk of which "are loosely slip-fitted into the exchanger tubes, together with a steam purge of the space between the exchanger tube sheet and the inlet cone tube sheet, the steam being supplied at a higher pressure than the heater effluent. In an alternative embodiment the inlet cone tube sheet is eliminated by using hexagonal tubes welded to each other. The steam effectively purges the cone area of any hydrocarbons which may enter. Because of the slip-fit of the inlet cone tubes within the transfer line exchanger tubes, the purged steam can pass around the outside of the inlet cone tubes and into the exchanger tubes. Also because of this feature, the tube sheet of the exchanger is not restricted in movement. Lastly, a much smaller quantity of insulation is required by the arrangement of the invention. In some instances, it may be desirable to weld some of the tubes to 3 simplify assembly and stabilize the position of the tubes in the cone.

Understanding of the invention will be facilitated by referring to the accompanying drawings, which are intended to be illustrations only and which are not to be interpreted in a limiting sense.

In the drawings:

FIGURE 1 is a cross-sectional elevation of a heater outlet, inlet cone and transfer line exchanger in accordance with the present invention; and

FIGURE 2 is an elevation of the inlet cone tube openings in an alternative embodiment of the invention.

With reference to FIG. 1, the heater outlet is indicated generally at 10, the inlet cone at 12, and the transfer line exchanger at 14. The heater outlet is provided with insulation 16, a protective sleeve 18 and a flange 20 for attachment to inlet cone 12. A suitable gasket 22 seals the joint.

Inlet cone 12 comprises a flanged steel shell 24 with some insulation 26 between heater outlet flange 20 and the inlet cone tube sheet 28. This tube sheet 28, which may be either dished, as shown, flat or dished in the reverse direction, supports a plurality of tubes 30, of which only a few are shown for ease of illustration. It will be.

understood that there are as many tubes 30 as there are tubes in exchanger 14. At at least one point on inlet cone 12 there is an opening 32 with a suitable fitting 34 for con nection to a source 36' of steam. This need not be especially high pressure steam, as long as it is superheated and ata pressure higher than the effluent gas from the heater. Inlet cone 12 may be externally insulated.

A second gasket 40 effects a seal between inlet cone 12 and exchanger 14. As shown, exchanger 14 comprises a shell 42 with suitable flanges, a tube sheet 44 supported therein and tubes 46 attached to tube sheet 44, but it will be understood that many different exchanger daigns are employed. The ends of tubes 30 extend into tubes 46, there being a loose, fluid-permeable fit therebetween.

The most efficient exchangers for this type of service have a large number of small diameter tubes. Double-wall tubes may sometimes be employed. The large number of tubes makes construction of tube sheet 28 difiicult, since almost all of the area is required for the tubes and there is very little area for supporting structure. And of course,

the closer tube sheet 28 can be located to the narrow end of thecone, the more effective the device will be. This problem is somewhat lessened,-however, by the fact that the tubes 30 are of somewhat smaller outside diameter than tubes 46.

This problem can be substantially reduced by employing tubes with hexagonal ends to fabricate tubes 30, as shown in FIG. 2. In this embodiment, the tubes are essentially self-supporting, being welded together to form number would be employed. It will also be understood that shield 50 need not be fabricated of metal, but may be refractory or a suitable packing material.

As noted hereinabove, the significant operating feature is that the steam pressure in area 38 be maintained at a higher level than the pressure of the heater efiluent. While the steam temperature is not considered critical, the steam must be free of entrained water to avoid thermal shock.

Various changes in the details, steps, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as defined in the appended claims. In particular, while the general shape 7 of the device is referred to herein as generally conical, it will be understood that it may in fact be pyramidal, tetragonal or any configuration which presents a small opening to the heater outlet and a large opening to the exchanger inlet.

What is claimed is: 1. A connector duct for passing :fluids to the tube side of a heat exchanger that comprises:

a generally conical conduitconnectable at its larger end to said heat exchanger around the periphery thereof;

tubes extending from each of the tubes of the heat ex changer into the narrower portion of said conduit; means'securing the ends of said tubes within the narrower portion of said'conduit in substantially fluid tight relation therewith; and means capable of supplying fluid at an elevated pressure to the interior of said conduit in the region between said heat exchanger and said securing means. 2. The connector duct as claimed in cl aim. 1, wherein said tubes extending through said conduit also extend into the tubes of said heat exchanger, the fit of the majority of said tubes being less than fluid-tight.

3. The connector duct as claimed in claim 1, wherein said securing means comprises a tube sheet secured around its periphery to said conduit, and having said extending tubes secured to openings therein.

4. The connector duct as claimed in claim 1, wherein said securing means comprises a rigid structure formed by securing said extending tubes to each other and to said conduit.

5. The connector duct as claimed in claim 4, wherein said extending tubes have hexagonal ends and said rigid structure is a honeycomb-type structure, and additionally comprising shield means filling the voids between said rigid structure and said conduit. 7

6. In combination with a fluid heater and a shell and tube heat exchanger, a connector conduit that comprises:

a generally conical conduit connected at its larger end to the tube side of said heat exchanger and connected at its smaller end to the outlet of said heater; tubes extending from each of the tubes of said heat exchanger into the narrower portion of said conduit,

s-aid extending tubes being of slightly smaller outa said securing means comprises a tube sheet secured around its periphery to said conduit, and having said extending tubes secured to openings therein. 7

8. The connector duct as claimed in claim 6, wherein said extending tubes have hexagonal ends and said securing means is a honeycomb-type structure, and additionally comprising shield means filling the voids between said securing means and said conduit.

References Cited .UNITED STATES PATENTS 9/1961 Laist 133.118 2/1967 Vollhardt --145 ROBERT A. OLEARY, Primary Examiner. C. SUKALO, Assistant Exam ner, 

